test: 添加 Utils 纯函数单元测试 (测试计划 02)

覆盖 xml, hash, stringUtils, semver, uuid, format, frontmatterParser,
file, glob, diff 共 10 个模块的纯函数测试。
json.ts 因模块加载链路过重暂跳过。
共 190 个测试用例（含已有 array/set）全部通过。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/utils/__tests__/stringUtils.test.ts

@@ -0,0 +1,195 @@
+import { describe, expect, test } from "bun:test";
+import {
+  escapeRegExp,
+  capitalize,
+  plural,
+  firstLineOf,
+  countCharInString,
+  normalizeFullWidthDigits,
+  normalizeFullWidthSpace,
+  safeJoinLines,
+  EndTruncatingAccumulator,
+  truncateToLines,
+} from "../stringUtils";
+
+describe("escapeRegExp", () => {
+  test("escapes special regex chars", () => {
+    expect(escapeRegExp("a.b*c?d")).toBe("a\\.b\\*c\\?d");
+  });
+
+  test("escapes brackets and parens", () => {
+    expect(escapeRegExp("[foo](bar)")).toBe("\\[foo\\]\\(bar\\)");
+  });
+
+  test("escapes all special chars", () => {
+    expect(escapeRegExp("^${}()|[]\\.*+?")).toBe(
+      "\\^\\$\\{\\}\\(\\)\\|\\[\\]\\\\\\.\\*\\+\\?"
+    );
+  });
+
+  test("returns normal string unchanged", () => {
+    expect(escapeRegExp("hello")).toBe("hello");
+  });
+});
+
+describe("capitalize", () => {
+  test("uppercases first char", () => {
+    expect(capitalize("hello")).toBe("Hello");
+  });
+
+  test("does NOT lowercase rest", () => {
+    expect(capitalize("fooBar")).toBe("FooBar");
+  });
+
+  test("handles single char", () => {
+    expect(capitalize("a")).toBe("A");
+  });
+
+  test("handles empty string", () => {
+    expect(capitalize("")).toBe("");
+  });
+});
+
+describe("plural", () => {
+  test("returns singular for 1", () => {
+    expect(plural(1, "file")).toBe("file");
+  });
+
+  test("returns plural for 0", () => {
+    expect(plural(0, "file")).toBe("files");
+  });
+
+  test("returns plural for many", () => {
+    expect(plural(3, "file")).toBe("files");
+  });
+
+  test("uses custom plural form", () => {
+    expect(plural(2, "entry", "entries")).toBe("entries");
+  });
+});
+
+describe("firstLineOf", () => {
+  test("returns first line of multiline string", () => {
+    expect(firstLineOf("line1\nline2\nline3")).toBe("line1");
+  });
+
+  test("returns whole string if no newline", () => {
+    expect(firstLineOf("single line")).toBe("single line");
+  });
+
+  test("returns empty string for leading newline", () => {
+    expect(firstLineOf("\nline2")).toBe("");
+  });
+});
+
+describe("countCharInString", () => {
+  test("counts occurrences of a character", () => {
+    expect(countCharInString("hello world", "l")).toBe(3);
+  });
+
+  test("returns 0 for no match", () => {
+    expect(countCharInString("hello", "z")).toBe(0);
+  });
+
+  test("counts from start offset", () => {
+    expect(countCharInString("aabaa", "a", 2)).toBe(2);
+  });
+
+  test("returns 0 for empty string", () => {
+    expect(countCharInString("", "a")).toBe(0);
+  });
+});
+
+describe("normalizeFullWidthDigits", () => {
+  test("converts full-width digits to half-width", () => {
+    expect(normalizeFullWidthDigits("０１２３４５６７８９")).toBe("0123456789");
+  });
+
+  test("leaves half-width digits unchanged", () => {
+    expect(normalizeFullWidthDigits("0123")).toBe("0123");
+  });
+
+  test("handles mixed content", () => {
+    expect(normalizeFullWidthDigits("test１２３")).toBe("test123");
+  });
+});
+
+describe("normalizeFullWidthSpace", () => {
+  test("converts full-width space to half-width", () => {
+    expect(normalizeFullWidthSpace("a\u3000b")).toBe("a b");
+  });
+
+  test("leaves normal spaces unchanged", () => {
+    expect(normalizeFullWidthSpace("a b")).toBe("a b");
+  });
+});
+
+describe("safeJoinLines", () => {
+  test("joins lines with delimiter", () => {
+    expect(safeJoinLines(["a", "b", "c"], ",")).toBe("a,b,c");
+  });
+
+  test("truncates when exceeding maxSize", () => {
+    const result = safeJoinLines(["hello", "world", "foo"], ",", 12);
+    expect(result.length).toBeLessThanOrEqual(12 + "...[truncated]".length);
+    expect(result).toContain("...[truncated]");
+  });
+
+  test("returns empty string for empty input", () => {
+    expect(safeJoinLines([])).toBe("");
+  });
+});
+
+describe("EndTruncatingAccumulator", () => {
+  test("accumulates text", () => {
+    const acc = new EndTruncatingAccumulator(100);
+    acc.append("hello ");
+    acc.append("world");
+    expect(acc.toString()).toBe("hello world");
+  });
+
+  test("truncates when exceeding maxSize", () => {
+    const acc = new EndTruncatingAccumulator(10);
+    acc.append("12345678901234567890");
+    expect(acc.truncated).toBe(true);
+    expect(acc.length).toBe(10);
+  });
+
+  test("reports total bytes received", () => {
+    const acc = new EndTruncatingAccumulator(5);
+    acc.append("1234567890");
+    expect(acc.totalBytes).toBe(10);
+  });
+
+  test("clear resets state", () => {
+    const acc = new EndTruncatingAccumulator(100);
+    acc.append("hello");
+    acc.clear();
+    expect(acc.toString()).toBe("");
+    expect(acc.length).toBe(0);
+    expect(acc.truncated).toBe(false);
+  });
+
+  test("stops accepting data once truncated and full", () => {
+    const acc = new EndTruncatingAccumulator(5);
+    acc.append("12345");
+    acc.append("67890");
+    expect(acc.length).toBe(5);
+    acc.append("more");
+    expect(acc.length).toBe(5);
+  });
+});
+
+describe("truncateToLines", () => {
+  test("returns text unchanged if within limit", () => {
+    expect(truncateToLines("a\nb\nc", 5)).toBe("a\nb\nc");
+  });
+
+  test("truncates text exceeding limit", () => {
+    expect(truncateToLines("a\nb\nc\nd\ne", 3)).toBe("a\nb\nc…");
+  });
+
+  test("handles single line", () => {
+    expect(truncateToLines("hello", 1)).toBe("hello");
+  });
+});